One typical example of a conventional commutator of a small-sized motor, for example, a fractional horsepower D.C. motor is shown in FIG. 3, which is a plan view thereof and FIG. 4, which is a perspective view thereof. As shown by FIG. 3 and FIG. 4 the conventional commutator is made by filling a metal pipe 1, provided with a specified number of risers 1a, with a body of plastic resin 2, which is molded and sets in place in the inside space of the metal pipe 1 and embraces the bases of the risers therein, then cutting shallow slots 3, which extend radially from and include the axis of the metal pipe 1, so that the metal pipe 1 is divided into a specified multiplicity of metal segments. In order to mechanically combine and hold the segments of the commutator in one rigid body, the center core portion 201 of the resin body 2 is retained uncut. Particularly, the slots are cut by advancing a cutting saw radially inwards by a specified small distance, into the resin body 2, toward the axis X of the metal pipe 1, in a manner to retain the central core part 20, uncut. Therefore, in the making of the conventional-type commutator, it is necessary to advance the saw or the like means and cut a slot 3 once each minus one total for the number of segments required. Thus, a considerable number of cuts, taking great care not to cut to an excessive depth are necessary. Furthermore, since a considerable number of the cuttings from generatrices on the slippery metal pipe face into the resin core are necessary, it is not easy to divide the metal pipe 1 into the segments with precise dividing angles around the axis. Besides, since each slot has a shallow bottom, metal powder dust of the commutator segment metal and/or brushes produced during the operation of the rotor incorporating the conventional commutator is likely to be filled and deposited in the slots, thereby causing short-circuiting of the segments.
Neither the metal nor the plastic resin used to make the commutator need depart from that used in the prior art. Typical uses for the commutator are such as those disclosed in the prior U.S. patent of Yokisada et al, U.S. Pat. No. 3,662,240 issued May 9, 1972.